Two kinetically distinct forms of hepatic pyruvate kinase whose interconversion is modulated by glucagon and insulin have been demonstrated in the perfused rat liver. These enzyme forms are kinetically distinguished by their dependence in the substrate, P-$nolpyruvate. At pH 7.5 and 2.5 mM ADP, (PEP)0.5 is 1.6 plus or minus 0.2 mM P-enolpyruvate (n equals 8) for the enzyme from livers perfused with no hormone or with insulin. (PEP)0.5 is 2.5 plus or minus 0.4 mM P-enolpyruvate (n equals 8) for the enzyme from livers perfused with 10 to the minus 7th power glucagon or 0.1 mM cyclic AMP. The proposed research will involve separating and purifying the two forms of hepatic pyruvate kinase and determining if the hormonal regulation involves phosphorylation dephosphorylation of the enzyme. The study will also investigate the biochemical events involved in the hormonal regulation of hepatic pyruvate kinase. The regulation of other hepatic enzymes, including fructose-1,6-bisphosphatase and glucokinase, in the perfused rat liver will also be studied.